The present invention relates to a swing-type actuator such as an actuator for magnetic disk drives, and more particularly to a swing-type actuator capable of swinging a function member such as a magnetic head along a circular course.
Conventionally, the positioning of a magnetic head on a recording track of a magnetic disk, etc. is conducted by a swing-type or rotation-type actuator as shown in FIGS. 4 and 5. In both figures, a yoke 1 is fixedly provided with permanent magnets 2, and a pair of yokes 1 are assembled by supports 3 such that different magnetic poles of the permanent magnets 2 are opposite each other via a magnetic gap 4 to form a magnetic circuit. 5 represents an arm having one end to which a flat movable coil 6 is fixed, and the other end to which a magnetic head (not shown) is fixed. The arm 5 is arranged such that the movable coil 6 located in the magnetic gap 4 can swing around a shaft 7. When an operation signal is supplied to the movable coil 6, a magnetic force generated from the movable coil 6 according to Fleming's left hand rule functions as an attraction force or a repulsion force to each permanent magnet 2, so that the arm 5 is rotated around the shaft 7. As a result, a magnetic head fixed to a tip end of the arm 5 is positioned on a desired magnetic track of a magnetic disk (not shown). The direction of the rotation of the arm 5 can be changed by inverting the direction of current applied to the movable coil 6.
There is also a conventional swing-type actuator shown in FIGS. 6 and 7, which is operated in the same manner as that shown in FIGS. 4 and 5. In this swing-type actuator, because only one of the yokes 1, 1 is provided with permanent magnets 2, 2, the total thickness of the actuator can be reduced. Incidentally, reference numerals in FIGS. 6 and 7 are the same as those in FIGS. 4 and 5, as long as they show the same parts.
In the above conventional actuators for magnetic disk drives, the movable coil 6 is usually fixed to the arm 5 by an adhesive. Incidentally, in the swing-type actuator shown in FIGS. 6 and 7, the arm 5 is fixed to a bobbin 8 having a bottom plate by screws [not shown], and the coil 6 is fixed within the bobbin 8 by an adhesive. However, the fixing of the movable coil 6 by an adhesive is sometimes troublesome, failing to provide accurate positioning of the movable coil 6. In addition, handling of terminals of the movable coil 6 is complicated, lowering the productivity of assembling of the arm 5. Since there is increasingly higher demand for miniaturization and reduction in thickness of magnetic disk drives, it is necessary to improve the positioning accuracy of the movable coil 6, and the productivity and reliability of fixing of the movable coil 6 to the arm 5. In this sense, the conventional arms fail to satisfy these requirements.
To solve the above problems, attempts have been made to integrally fix a movable coil 6 to an arm 5 by an integral resin molding (for instance, Japanese Utility Model Laid-Open No. 60-159556 and U.S. Pat. No. 4,855,853). In such a structure, the movable coil can be supported by a simplified structure, and the thickness of the movable coil can be extremely reduced. Accordingly, such a structure is advantageous for miniaturizing actuators.
However, since the arm 5 is generally made of aluminum alloy by die casting, it has a large specific gravity. Accordingly, it needs a large driving electric power and suffers from a poor response speed.
Recently, portable information and communications equipment have been finding widespread applications, and in such equipment miniaturization, reduction of weight and energy consumption are required much more than in the conventional stationary equipment. Also, a driving actuator having a high response speed is necessary in such equipment. However, the conventional actuators fail to meet such requirements.